Featured Research

from universities, journals, and other organizations

'Jekyll and Hyde' star morphs from radio to X-ray pulsar and back again

Date:

September 25, 2013

Source:

National Radio Astronomy Observatory

Summary:

Astronomers have uncovered the strange case of a neutron star with the peculiar ability to transform from a radio pulsar into an X-ray pulsar and back again. This star's capricious behavior appears to be fueled by a nearby companion star and may give new insights into the birth of millisecond pulsars.

Astronomers have uncovered the strange case of a neutron star with the peculiar ability to transform from a radio pulsar into an X-ray pulsar and back again. This star's capricious behavior appears to be fueled by a nearby companion star and may give new insights into the birth of millisecond pulsars.

Related Articles

"What we're seeing is a star that is the cosmic equivalent of 'Dr. Jekyll and Mr. Hyde,' with the ability to change from one form to its more intense counterpart with startling speed," said Scott Ransom, an astronomer at the National Radio Astronomy Observatory (NRAO) in Charlottesville, Va. "Though we have known that X-ray binaries -- some of which are observed as X-ray pulsars -- can evolve over millions of years to become rapidly spinning radio pulsars, we were surprised to find one that seemed to swing so quickly between the two."

Neutron stars are the superdense remains of massive stars that have exploded as supernovas. This particular neutron star, dubbed IGR J18245-2452, is located about 18,000 light-years from Earth in the constellation Sagittarius in a cluster of stars known as M28. It was first identified as a millisecond radio pulsar in 2005 with the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) and then later rediscovered as an X-ray pulsar by another team of astronomers in 2013. The two teams eventually realized they were observing the same object, even though it was behaving very differently depending on when it was observed. Additional observations and archival data from other telescopes confirmed the on-again, off-again cycle of X-ray and radio pulsations.

"Various observations of one particular star over the years and with different telescopes have revealed vastly different things -- at one time a pulsar and the other an X-ray binary," said Alessandro Papitto of the Institute of Space Sciences (Consejo Superior de Investigaciones Cientificas -- Institut d'Estudis Espacials de Catalunya) in Barcelona, Spain, and lead author of a paper published in the journal Nature. "This was particularly intriguing because radio pulses don't come from an X-ray binary and the X-ray source has to be long gone before radio signals can emerge."

The answer to this puzzle was found in the complex interplay between the neutron star and its nearby companion.

X-ray binaries, as their name implies, occur in a two-star system in which a neutron star is accompanied by a more normal, low-mass star. The smaller but considerably more massive neutron star can draw off material from its companion, forming a flattened disk of gas around the neutron star. Gradually, as this material swirls down to the surface of the neutron star, it becomes superheated and generates intense X-rays.

Astronomers believed that this process of accretion continued, mostly unabated, for millions of years. Eventually, the material would run out and the accretion would stop, along with the X-ray emission.

Without the influx of new material, the neutron star's powerful magnetic fields are able to generate beams of radio waves that sweep across space as the star rotates, giving the pulsar its characteristic lighthouse-like appearance.

Most radio pulsars rotate a few tens of times each second and -- if left to their own devices -- will slow down over many thousands of years. If the neutron star begins life as an X-ray binary, however, the matter accumulating on its surface causes the neutron star to "spin up," increasing its rate of rotation until it spins hundreds of times each second. When this accretion process stops, the result is a millisecond pulsar.

During their observations, the researchers detected outbursts of X-ray pulsations that went on for approximately one month and then abruptly stopped. Within a few days, the radio pulses once again emerged. These wild swings indicated that the material from the accretion disk was falling onto the neutron star in fits and starts, rather than in a long and constant stream as astronomers theorized.

An earlier study of another system with the GBT detected the first evidence of an accretion disk around a neutron star, which helped establish the link between low-mass X-ray binaries and pulsars.

The new data support this link but also show for the first time that the evolution process, which was thought to take perhaps millions of years, is actually more complex and can occur in episodic bursts that can last just a few days or weeks. "This not only demonstrates the evolutionary link between accretion and rotation-powered millisecond pulsars," said Ransom, "but also that some systems can swing between the two states on very short timescales."

The X-ray source was discovered by the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) and follow-up X-ray observations were performed by the XMM-Newton, Swift, and Chandra satellites. Radio observations were made by the GBT, the Parkes radio telescope, the Australia Telescope Compact Array, and the Westerbork Synthesis Radio Telescope.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

National Radio Astronomy Observatory. "'Jekyll and Hyde' star morphs from radio to X-ray pulsar and back again." ScienceDaily. ScienceDaily, 25 September 2013. <www.sciencedaily.com/releases/2013/09/130925132207.htm>.

National Radio Astronomy Observatory. (2013, September 25). 'Jekyll and Hyde' star morphs from radio to X-ray pulsar and back again. ScienceDaily. Retrieved March 31, 2015 from www.sciencedaily.com/releases/2013/09/130925132207.htm

National Radio Astronomy Observatory. "'Jekyll and Hyde' star morphs from radio to X-ray pulsar and back again." ScienceDaily. www.sciencedaily.com/releases/2013/09/130925132207.htm (accessed March 31, 2015).

More From ScienceDaily

More Space & Time News

Featured Research

Mar. 31, 2015 — Designed to detect the fossil radiation of the Universe, the Planck satellite, working in tandem with Herschel, can also help to understand the macrostructure of the Universe. A just-published ... full story

Mar. 31, 2015 — Astronomers have conducted observations of the massive-star forming region IRAS 16547-4247. The observation results shows the presence of multiple, or at least two, gas outflows from a protostar, ... full story

Mar. 30, 2015 — Stars form when gravity pulls together material within giant clouds of gas and dust. But gravity isn't the only force at work. Both turbulence and magnetic fields battle gravity, either by stirring ... full story

Mar. 30, 2015 — Scientists have long puzzled over the planet Mercury's excessively dark surface. New research suggests that carbon from passing comets could be the planet's mystery darkening ... full story

Mar. 30, 2015 — Luke Skywalker's home in "Star Wars" is the desert planet Tatooine, with twin sunsets because it orbits two stars. So far, only uninhabitable gas-giant planets have been identified circling such ... full story

Mar. 26, 2015 — Astronomers have studied how dark matter in clusters of galaxies behaves when the clusters collide. The results show that dark matter interacts with itself even less than previously thought, and ... full story

Mar. 26, 2015 — The best observations so far of the dusty gas cloud G2 confirm that it made its closest approach to the supermassive black hole at the centre of the Milky Way in May 2014 and has survived the ... full story

Mar. 25, 2015 — Researchers have completed a new analysis of an ancient Martian lake system in Jezero Crater, near the planet's equator. The study finds that the onslaught of water that filled the crater was one of ... full story

Mar. 25, 2015 — The precise measurement of Saturn's rotation has presented a great challenge to scientists, as different parts of this sweltering ball of hydrogen and helium rotate at different speeds whereas its ... full story

Jan. 8, 2015 — In an interstellar race against time, astronomers have measured the space-time warp in the gravity of a binary star and determined the mass of a neutron star--just before it vanished from ... full story

Feb. 20, 2014 — Scientists have found evidence that a tiny star called PSR J0738-4042 is being pounded by asteroids -- large lumps of rock from space. The environment around this star is especially harsh, full of ... full story

Feb. 2, 2012 — Pulsars are among the most exotic celestial bodies known. They have diameters of about 20 kilometers, but at the same time roughly the mass of our sun. A sugar-cube sized piece of its ultra-compact ... full story

Nov. 3, 2011 — Astronomers have tracked down the first gamma-ray pulsar in a globular cluster of stars. It is around 27,000 light years away and thus also holds the distance record in this class of objects. ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.